Reason #1: You'll Want to Exercise

Your 2013 get-fit plan got old faster than "Gangnam Style"? Breathe some fresh air into a tired routine (hey, the weather's on your side), and chances are, you won't blow off your next workout.

The Proof You're 23 percent more likely to repeat an outside session, or so an Ohio State University study suggests. A group of twentysomething women compared doing the same workout (they were walkers) indoors versus out, and no-walls won because it felt more, wait for it, fun!

Reason #2: No More I-Can't-Sleep Nights

Choose a sunrise workout and you could fall asleep when you want at night—up to an hour sooner.

The Proof Natural a.m. light resets circadian rhythms, so it may be easier to nod off, say experts at the Lighting Research Center in Troy, New York. Avoid a sunset session; it can delay melatonin release, making it tougher.

Reason #5: Genius Will Strike

But you've gotta leave your gadgets at home.

The Proof After a four-day hike sans tech, people did 50 percent better on a creativity test. University of Utah researchers say an hour of nature time yields some bennies, if you unplug. Smarter without a smartphone.

Reason #8: You'll Zen Out

You know that sense of peace you get jogging in a park? Not your imagination.

The Proof Exercisers reported being less tense and tired, and calmer, during any activity done outside rather than in, probably because those surroundings felt more serene, a Santa Clara University study notes.